| Epidemiological evidence suggests that exposure to the metalloid arsenic constitutes a risk factor for cardiovascular disease. Some of the cardiovascular effects attributed to arsenic are decreased cardiac function, peripheral vascular diseases and atherosclerosis. While the epidemiological evidence linking arsenic to cardiovascular (CVD) is abundant, the mechanisms of action are primarily unknown. The purpose of this study is to begin elucidating those mechanisms by (1) defining the changes in key atherogenic regulatory molecules upon exposure to arsenic in bovine aortic endothelial cells (BAE); (2) investigating the effects of arsenite on the formation of reactive oxygen (ROS) and reactive nitrogen species (RNS) in endothelial cells and (3) determining the effects of arsenite on atherogenesis and expression of key CVD regulatory molecules in the ApOE−/−/LDLr−/− atherosclerotic mouse model. This model develops severe atherosclerotic plaques early in life. We were able to use them in our studies to show the first laboratory-controlled evidence that arsenic increases the severity of arterial occlusion indicative of atherosclerosis. In order to understand the mechanisms behind this occurrence, we looked at various components of atherogenesis that might be influenced by the presence of arsenic. Sodium arsenite, the reduced form of inorganic arsenic was used in these studies. We found that production of peroxynitrite, a strong oxidant formed from the coupling of nitric oxide and superoxide anion, is significantly increased in BAE cells exposed to sodium arsenite. In addition, the biological marker for peroxynitrite, 3-nitrotyrosine, is increased in the atherosclerotic plaque of arsenite treated ApOE−/− /LDLr−/− mice. Expression of the inflammatory mediator, cyclooxygenase-2 (COX-2) is also upregulated in response to arsenite exposure, indicating an increase in the inflammatory response in BAE cells. This result was supported by an increase in the generation of prostaglandin E2 (PGE2) following exposure to arsenite in BAE cells. There was also an increase in the synthesis of the COX-2 product, prostaglandin I2 (PGI2), in the serum of arsenite exposed mice, although we were unable to detect an increase in PGE2 in this model. Since peroxynitrite is capable of nitrating protein tyrosine residues, peroxynitrite formation can be confirmed by determining the extent of nitrotyrosine formation in a protein. Nitration of COX-2 was detected in arsenite-treated cells, but not in untreated control cells, supporting the evidence that an increase in peroxynitrite results from arsenite exposure in BAE cells. Furthermore, an increase in the proinflammatory protein 5-lipoxygenase (5-Lo) results from arsenite exposure in BAE cells. This is mirrored by an increase in LTE 4, a product of the 5-Lo pathway, in the serum of mice chronically exposed to arsenite as well as in BAE cells. The findings in this report show that arsenic definitively increases the severity of occluded arteries in atherogenic mice and suggests an increase in reactive species, notably peroxynitrite, in BAE cells exposed to arsenic. Furthermore, induction of important inflammatory mediators such as COX-2 and 5-Lo may exacerbate the inflammatory state typical of atherosclerosis. |
